1. Field of Invention
This invention relates generally to space temperature conditioning systems and in particular to a new and improved method of determining refrigerant charge level in a space temperature conditioning system.
2. Background Art
Space temperature conditioning systems of the type having a refrigerant as a heat transfer medium are well-known in the art. It is important that such systems have a proper charge of refrigerant in order to function properly. Various methods of determining refrigerant charge level are known in the art. Most of these prior art methods provide only a qualitative determination of whether the charge level is below or above acceptable limits or require inputs from multiple sensors, including ambient temperature and humidity sensors, in order to determine refrigerant charge level, which increases the cost and complexity of the system. Examples of such prior art refrigerant charge level determination methods are shown in U.S. Pat. Nos. 4,381,549; 4,677,830; 5,239,865; 5,987,903; and 6,101,820.
There is, therefore, a need for an improved method of determining refrigerant charge level in a space temperature conditioning system. There is also a need for a method of determining refrigerant charge level in a space temperature conditioning system that is both relatively inexpensive and reliable under a wide range of ambient temperature conditions.
In accordance with the present invention, a method for determining refrigerant charge level in a space temperature conditioning system is provided. The method is comprised of the following steps: (a) establishing a relationship between at least one system operating parameter and refrigerant charge level, independent of ambient temperature conditions; (b) operating the space temperature conditioning system; (c) measuring the operating parameter(s) while the system is in operation; and (d) determining refrigerant charge level based on the established relationship in response to the measuring step.
In accordance with one embodiment of the invention, the establishing step comprises: (i) operating the system; (ii) measuring the operating parameter(s) under a plurality of ambient temperature conditions for each of a plurality of known refrigerant charge levels; and (iii) correlating the measured values of the operating parameter(s) to establish a relationship between refrigerant charge level and the operating parameter(s), independent of the ambient temperature conditions.
In accordance with another embodiment of the invention, the system is a space temperature conditioning system of the type having a condenser, an evaporator and a compressor for circulating a vapor compression refrigerant between the evaporator and the condenser and the at least one system operating parameter includes refrigerant subcooling.
In accordance with yet another embodiment of the invention, the at least one operating parameter includes refrigerant subcooling and refrigerant superheat.
In accordance with still another embodiment of the invention, the at least one operating parameter includes refrigerant subcooling and refrigerant pressure at at least one selected location in the system.
In accordance with the preferred embodiment of the invention, the at least one system operating parameter includes refrigerant subcooling, refrigerant superheat, liquid refrigerant pressure on a discharge side of the condenser and vapor refrigerant pressure on a suction side of the compressor. These four parameters are measured while the system is operating at a relatively steady-state condition and the measured values of the parameters are used to determine refrigerant charge level based on the predetermined relationship between charge level and each of these parameters. A human-detectable indication is provided regarding whether the charge level is within acceptable limits and if it is not within acceptable limits, the amount of the undercharge or overcharge condition is indicated.